Electric discharge device



y 1942. A. J. KLING 2,283,639

ELECTRIC DISCHARGE DEVICE Filed Sept. 26, 1941 Fig. 2.

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Inventor. I August J. Kl/jhgg, y His Attorney.

Patented May 19, 1942 f r NT orric 2,283,639 ELECTRIC DISCHARGE DEVICE August 5. Kling, Scotia, N. Y., assignor to General Electric Company, a corporation of New York Application September 26, 1941, Serial No. 412,377

G'Claims. (crest-27.5)

satisfactorily insofar as their emitting properties are concerned, but the use of such cathodes is complicated by the consideration that the resistance-heating means employed require relatively large currents for their successful operation. In large constructions this means that very heavy lead-in wires must be employed for supplying the heating current and this, in turn, requires the use of complicated and costly means for sealing these wires through the wall of the discharge space.

It has been proposed to mitigate the aforementioned difficulties by the use of bombardment heated cathode arrangements. However, this expedient, as heretofore practiced, has shown no practical advantage in gas-filled devices for the reason that a bombarding discharge produced in such a device operates as a low-voltage arc, incapable of maintaining emitting temperatures unless excessive currents are employed.

It is an object of the present invention to provide an improved form of bombardment-heatedcathode which inherently has a high voltage, lowcurrent characteristic and which is adapted for use in a gas-filled discharge tube.

According to a preferred embodiment of the invention the foregoing object is attained by means of a construction in which the cathode includes as a component part thereof a sealed highly evacuated container having within it an auxiliary electron emitter adapted to produce a heat-generating discharge tothe wall of the container. Because of the vacuum condition specified, the heating discharge may be of spacecharge limited character and can therefore take place at a high voltage. Accordingly, a relatively great heating effect can be obtained with a relatively low current in the discharge stream.

The features which I desire to protect herein are pointed out with particularity in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the drawing in which Fig. 1 is a sectional view of a discharge device suitably embodying the invention; Fig. 2

is a fragmentary sectional view illustrating a modification of the invention; and Fig. 3 is a section taken on line 3-3 of Fig. 2.

Referring-particularly to Fig. 1\, there is shown a discharge device comprising an elongated glass envelope H) which is of hermetically sealed construction. The envelope contains a substantial quantity of an ionizable medium, which may be either a fixed gas such as argon, neon, or the like,

or a vapor-producing substance such as mercury.

When mercury is used, it may be introduced in the form of a small globule as indicated at l I, this globule serving to maintain a vapor pressure of a few microns to a few millimeters of mercury during the operation of the tube.

- At the upper end of the discharge vessel and within the gas-filled space there is providedan anode l3 which is represented as being in the form of a bell-shaped body of graphite. This is cooperatively positioned with respect to a cathode structure, designated as a whole by the numeral I5.

In accordance with the present invention, the cathode l5 includes a sealed, highly evacuated metal container in the form of an elongated cylindrical shell llwhich is closed at its lower end by means of a header I8 welded or otherwise hermetically joined to the shell. A- metal tubulation I 9 extending from the bottom of the header serves as a means for evacuating the enclosed'space during fabrication of the cathode.

7 Within the metallic shell I! and substantially coaxial with it there is provided an electron emitter 29 which comprises a coiled filament of tungsten or other refractory metal, preferably coated with an activating material such as an alkaline earth oxide. The filament 26 is supported between appropriately positioned conduce tors 22 and 23 which are sealed through the header 18 by means of vacuum-tight seals indi cated at 24 and 25. Each of these seals comprises a metal eyelet secured to the header l8 and closed at its lower extremity by means of a body of glass fused into the eyelet. A further current supply conductor 28 is secured directly to the bottom of the header l8 and serves to supply current to the cathode structure as a whole. The various conductors 22, 23 and 28 are sealed through the discharge vessel ill by means of a conventional stem press 39 from which the cathode structure as a whole is supported.

The conductive shell I! is constituted of a metal such as nickel or molybdenum which is adapted for high temperature operation and is coated on its external surface with a thermionically active material such as an alkaline earth oxide or the like so that the shell is adapted to serve as a source of electrons for producing a discharge to the anode I3. In the use of the device, heating current is supplied to the electron emitter 20 through conductors 22 and 23, and an appropriate potential dilference is impressed betweenthese conductors and the conductor 28 so as to establish a discharge from the emitter to the interior wall surface of the shell Due to the highly evacuated condition of the space within which the emitter is contained (the vacuum should preferably be less than one micron), this dischargeis of space charge limited character and may accordingly take place at high voltage. For this reason the electrons taking part in the discharge attain high kinetic energy within the discharge space, so that a relatively small electron flow is adequate to produce intense heating of the surfaces .of the part [1. Accordingly only a relatively small current needs to be supplied to the filament 20, and the lead-in conductors associated with the heating circuit for the emitter may be of relatively small dimensions and low currentcarrying capacity. -This consideration greatly simplifies the problem of sealing these conductors into the discharge vessel It and minimizes the likelihood of fracture of the lead-in seals due tovintense localized heating.

In order still further to conserve heating energy and to make thecurrent supply requirements as small as possible, a. heat shield 33 is preferably placed around the cathode shell I! so as to minimize radiation from its emitting surfaces.

The invention may also be used in connection with indirectly heated cathode arrangements, and one such arrangement is illustrated in Fig. 2. In this case the principal emitting surfaces of the cathode (shown as being contained within the lower portion of a discharge vessel 40) are provided by a plurality of vane structures 42 enclosed within a cylindrical heat shield 43. At their inner edges the vanes 42 abut against a cylindrical metallic container 45 which comprises a sealed, evacuated enclosure generally similar to the shell I! of Fig. 1. As in the arrangement described in connection with Fig. 1, the container 45 encloses a filamentary electron emitter 47 which has lead-in conductors 48 and 49 sealed through the lower end of the container.

In the operation of the device of Fig. 2 heating current is passed through the filamentary emitter 4! and a discharge is established to the wall of the container 45, thereby raising the body of the container to an elevated temperature. The heat thus generated is communicated by conduction and radiation to the vanes 42, thus bringing them to a temperature of effective electron emissivity. In order that the resultant electron current may be as high as possible, it is desirable that the vanes 42 be coated with an emissionenhancing material such as an alkaline earth oxide.

While the invention has been described by reference to particular embodiments thereof, it will be understood that numerous modifications may be made by those skilled in the art without actually departing from the invention. 1, therefore, aim in the appended claims to cover all such equivalent variations as come within the true spirit and scope of the foregoing disclosure.

What I claim as new and desire to secure by yLetters Patentv of the United States, is:

component thereof a member which forms a wall part of a highly evacuated discharge enclosure and further including an electron emitter within said enclosure for producing a heat-generating discharge to said wall part.

2. In combination, a discharge vessel containing an ionizable medium at a substantial pressure, an anode within the vessel, a cathode cooperatively positioned with respect to the anode, and means for maintaining the active parts of the cathode at a temperature of thermionic emission, said means including a cathode component which forms a wall part of a highly evacuated discharge enclosure and an electron emitter within the enclosure for producing a heatproducing discharge to the said Wall part.

3. In combination, a discharge Vessel containing an ionizable medium at a substantial pressure, an anode Within the vessel, and a thermionic cathode cooperatively positioned with respect to the anode, said cathode including a sealed, evacuated metal container extending within the said discharge vessel and an electron emitter within the container for producing a discharge to the container to maintain the cathode at a temperature of thermionic emission.

4. A discharge device comprising a closed vessel which contains a substantial quantity of an ionizable medium, an anode within the said vessel, and a cathode cooperatively positioned with respect to the anode, said cathode comprising a sealed, highly-evacuated container, a thermionic electron-emitter within the container for producing a discharge to the container of suificient intensity to maintain the container at a temperature of effective electron emissivity, and lead-in conductor sealed through the walls of both the said vessel and the said container for supplying heating current to the electron-emitter.

5. In combination, a discharge vessel containing a substantial quantity of an ionizable medium, an anode within the vessel, a sealed evac-I uated metallic container also within the vessel and cooperatively positioned with respect to the anode, said container being provided externally with an electron-emissive material whereby it is enabled to function as a cathode, and an electron emitter within the eva'cuated space enclosed by the container for producing a heat-generating discharge therein of suflicient intensity to maintain the said emissive material at a temperature of effective thermionic emission 6. A discharge device comprising a closed vessel which contains a substantial quantity of an ionizable medium, an anode within the vessel, a cathode comprising extended electron-emitting surfaces cooperatively positioned with respect to the anode, and means for maintaining the said surfaces at a. temperature of thermionic emissivity, said means comprising a sealed evacuated metal container in effective heat-exchanging relation with the said surfaces, and an electron emitter within the vacuum space enclosed by the container for producing a heat-generating discharge to the container.

. AUGUST J. KLING. 

